Tablets, and specifically the iPad from Apple, have been one of the big drivers for growth in mobile in the last couple of years, but figures out today from NPD indicate that their popularity is going to get even bigger: the market for tablets, its researchers predict, is set to boom from 121 million shipped tablets today to 416 million devices by 2017, when they will overtake notebooks to become the most popular mobile PC device, driven by a drop in costs and a rise in features.

The rise of tablets is also a story about the decline of notebooks. The market for these will continue to expand, but at a rate lower than the 28 percent that tablets will see: NPD says that by 2017 there will be 393 million notebooks shipped compared to 208 million today.

One takeaway from this: although Apple with its iPad line of tablets has dominated the tablet world in market and mindshare up to now, the space is far from penetrated, and that means that companies like Microsoft, Google and others still have a lot to play for.

Part of the reason we will see a lot of features continue to be incorporated into tablets is because of the emphasis of content on the devices. App stores are increasingly catering to tablet users.

But by the way, this is not to say notebooks are dying. Far from it — they will still account for 49 percent of the mobile PC market, NPD says, shipping 393 million units in 2017 compared to 208 million in 2012. It adds that notebook makers are also taking heed and looking to put more tablet-like features into their products — for example, becoming thinner and incorporating touch functionality.